III.

Context: Ankle sprains are among the most common musculoskeletal injuries, and many individuals with ankle sprains develop chronic ankle instability (CAI). Individuals with CAI exhibit proprioceptive and postural-control deficits, as well as altered osteokinematics, during gait. Neuromuscular activity is theorized to play a pivotal role in CAI, but deficits during walking are unclear.Objective: To compare motor-recruitment patterns as demonstrated by surface electromyography amplitudes between participants with CAI and healthy control participants during walking.Design: Descriptive laboratory study. Setting: Laboratory.Patients or Other Participants: Fifteen adults with CAI (5 men, 10 women; age ¼ 23 6 4.2 years, height ¼ 173 6 10.8 cm, mass ¼ 72.4 6 14 kg) and 15 matched healthy control adults (5 men, 10 women; age ¼ 22.9 6 3.4 years, height ¼ 173 6 9.4 cm, mass ¼ 70.8 6 18 kg).Intervention(s): Participants walked shod on a treadmill while surface electromyography signals were recorded from the anterior tibialis, peroneus longus, lateral gastrocnemius, rectus femoris, biceps femoris, and gluteus medius muscles.Main Outcome Measure(s): Preinitial contact amplitude, postinitial contact amplitude, time of activation relative to initial contact, and percentage of activation time across the stride cycle were calculated for each muscle.Results: Time of activation for all muscles tested occurred earlier in the CAI group than in the control group. The peroneus longus was activated for a longer duration across the entire stride cycle in the CAI group (36.0% 6 10.3%) than the control group (23.3% 6 22.2%; P ¼ .05). No differences were noted between groups for measures of electromyographic amplitude at either preinitial or postinitial contact (P . .05).Conclusions: We identified differences between the CAI and control groups in the timing of muscle activation relative to heel strike in multiple lower extremity muscles and in the percentage of activation time across the entire stride cycle in the peroneus longus muscle. Individuals with CAI demonstrated neuromuscular-activation strategies throughout the lower extremity that were different from those of healthy control participants. Targeted therapeutic interventions for CAI may need to be focused on restoring normal neuromuscular function during gait.

Lateral ankle sprains (LAS) have been reported as one of the most common musculoskeletal injuries observed in sports and in individuals who are recreationally active. Approximately 40% of individuals who sustain a LAS develop a condition known as chronic ankle instability (CAI). Years of research has identified numerous impairments associated with CAI such as decreases in range of motion (ROM), strength, postural control, and altered movement patterns during functional activities when compared to individuals with no LAS history. As a result, an impairment-based rehabilitation model was developed to treat the common impairments associated with CAI. The impairment-based rehabilitation model has been shown to be an effective rehabilitation strategy at improving both clinical and patient-oriented outcomes in patients with CAI. To date, the efficacy of an impairment-based rehabilitation model has not been evaluated in patients with an acute LAS. Prior to implementing an impairment-based model for the treatment of an acute LAS, similarities between impairments associated with acute LAS and CAI across the spectrum of the healing process is warranted. Therefore, the purpose of this review paper is to compare and contrast impairments and treatment techniques in individuals with an acute LAS, sub-acute LAS, and CAI. A secondary purpose of this review is to provide clinical commentary on the management of acute LAS and speculate how the implementation of an impairment-based rehabilitation strategy for the treatment of acute LAS could minimize the development of CAI. The main findings of this review were that similar impairments (decreased ROM, strength, postural control, and functional activities) are observed in patients with acute LAS, sub-acute LAS, and CAI, suggesting that the impairments associated with CAI are a continuation from the original impairments developed during the initial LAS. Therefore, the use of an impairment-based model may be advantageous when treating patients with an acute LAS.

Patients with CAI demonstrated decreased muscle activity of ankle, knee, and hip musculature during common functional rehabilitative tasks. Clinicians may benefit from implementing functional exercises for patients with CAI that target both distal and proximal muscles of the lower extremity.

Context: The intrinsic foot muscles maintain the medial longitudinal arch and aid in force distribution and postural control during gait. Impaired intrinsic foot-muscle function has been linked to various foot conditions. Several rehabilitative exercises have been proposed to improve it; however, literature that identifies which individual muscles are activated during specific intrinsic foot-muscle exercises is lacking.Objective: To describe changes in activation of the intrinsic plantar foot muscles after 4 exercises as measured with T2 magnetic resonance imaging (MRI).Design: Descriptive laboratory study. Intervention(s): Participants underwent T2 MRI before and after each exercise. They completed 1 set of 40 repetitions of each exercise (short-foot exercise, toes spread out, first-toe extension, second-to fifth-toes extension).Main Outcome Measure(s): Percentage increases in muscle activation of the abductor hallucis, flexor digitorum brevis, abductor digiti minimi, quadratus plantae, flexor digiti minimi, adductor hallucis oblique, flexor hallucis brevis, and interossei and lumbricals (analyzed together) after each exercise were assessed using T2 MRI.Results: All muscles showed increased activation after all exercises. The mean percentage increase in activation ranged from 16.7% to 34.9% for the short-foot exercise, 17.3% to 35.2% for toes spread out, 13.1% to 18.1% for first-toe extension, and 8.9% to 22.5% for second-to fifth-toes extension. All increases in activation had associated 95% confidence intervals that did not cross zero.Conclusions: Each of the 4 exercises was associated with increased activation in all of the plantar intrinsic foot muscles evaluated. These results may have clinical implications for the prescription of specific exercises to target individual intrinsic foot muscles.Key Words: short-foot exercise, muscle functional magnetic resonance imaging, toes spread out, medial longitudinal arch Key PointsClinicians can prescribe the short-foot exercise, toes-spread-out exercise, first-toe-extension exercise, and secondto fifth-toes-extension exercise to activate the intrinsic foot muscles. These exercises can result in a 9% to 35% increase in intrinsic foot-muscle activity.